The proposed work is to elucidate the chemical and pharmacological nature of algal and other aquatic toxins which have serious impact on public health and provide basic information required to design preventive measures, and at the same time it is intended to discover new site-specific toxins as tools to investigate important biological mechanisms with an ultimate intention to elucidate the structure and function of neural receptors suh as sodium channels. Specifically, the isolation, structure determination and pharmacological evaluation of 1) paralytic shellfish poisons (PSP) and related toxins found in Gonyaulax spp. and other organisms, 2) neurotoxic shellfish poisons (NSP) produced by the Florida red tide organisms, Gymnodinium breve, 3) the hepatotoxins in the blue-green alga, Microcystis aeruginosa, which sometimes threatens public water systems, 4) an unidentified toxin which was involved in the mass shellfish poisoning in New York and New England, are planned. The toxins will be isolated from the mass-cultured organisms and/or those organisms which accumulated the toxins in the food chain. Pharmacological and neurophysiological studies of the isolated toxins will be carried out in collaboration with specialists. The derived knowledge will be disseminated to health officials and other concerned parties.